Transistor



TRANSISTOR Filed Feb. 14, 1957 m luxlww INVENTOR s LOUIS MARIUS NIJLANDJAN ADRlAN US MANINTVELD BY 7 2 Z 2 I 4 AGENT United States Patent OTRANSISTOR Application February 14, 1957, Serial No. 640,212

Claims priority, application Netherlands February 29, 1956 9 Claims.(Cl. 317-234) The invention relates to a method of producing asemiconductive electrode system, more particularly a transistor, inwhich a semi-conductive body .of, for example, germanium or silicon isprovided with at least one rectifying electrode and an ohmic connection,this structure being then etched and housed in an envelope.

The invention furthermore relates to a semi-conductive electrode system,more particularly a transistor, housed in an airtight'envelope.

The invention has been found to be of particular importance fortransistors, for the purpose of increasing the current amplificationfactor ea which is defined by the equation:

wherein I and l designate the collector current and the base currentrespectively, measured at a constant collector voltage V It is alreadyknown that the current amplification factor of germanium transistors andparticularly of silicon transistors can be enhanced by coating theirsemi-conductive surfaces with a layer of oxidizing material, forexample, lead minium, zinc chromate or strontium chromate, and,furthermore, that organic compounds may be used for this purpose. Byexperiments it has been found, however, that the transistors thusmanufactured are often not stable at higher temperatures.

The invention has for its object to provide inter alia a method by whicha semi-conductive electrode system having a high current amplificationfactor and great stability can be manufactured. It has furthermore theadvantage that, in a simple manner, the surface of the semiconductivebody can be coated with very thin, effective layers even of molecularthickness.

In accordance with the invention the semi-conductive body with itselectrode and ohmic connection is introduced, subsequent to the etchingoperation, into a milieu containing at least a nitrogen-oxygen compound.

Use is preferably made of a nitrogen-oxygen compound which containsmolecules of N and N 0 the equilibrium shifting in the direction of thefirst-mentioned compound at higher temperatures. In order to increasethe effect water vapour may also be added.

It is further noted that the results obtainable by the method accordingto the invention are in general not dependent upon the special etchingsolution'employed.

Although the invention is not restricted to a particular semi-conductivesubstance, it is particularly suitable for use with semi-conductiveelectrode systems, for example, alloy transistors, of which thesemi-conductive body consists of silicon, since by the conventionalmeans, which in the case of germanium yielded satisfactory values of thecurrent amplification factor, unsatisfactory results are obtained in thecase of silicon.

A particular embodiment of the invention consists in that thesemi-conductive body with its electrode ,and ohmic connection isarranged in a vacuum-tight envelope 2,887,630 Patented May 19, 1959containing at least one nitrogen-oxygen compound and, if desired, watervapour. With silicon transistors an additional effect is obtained, ifthe gaseous mixture in the envelope, before this envelope is finallyclosed, is pumped oif partly, preferably down to a pressure of less than10- mm. Hg.

A particular embodiment of a semi-conductive electrode system,especially a transister according to the invention, contains in thevacuum-tight envelope at least one nitrogen-oxygen compound. There mayfurthermore be water vapour in the envelope.

It should be noted that the favourable effect of such a gaseous milieuor atmosphere is, of course, not restricted to transistors, but thatsimilar effects will be obtained when the invention is applied to othersemi-conductive electrode systems.

By way of example one embodiment of a semi-conduc tive electrode systemaccording to the invention will now be described with reference to thesole figure in the accompanying drawing, which shows in cross-section, atransistor according to the invention.

Referring now-to the figure, the transistor comprises a thinsemi-conductive disc 1 provided with an emitter electrode 2, a collectorelectrode 3 and an annular ohmic base connection 4. The electrodes 2 and3 and the ohmic connection 4 are each connected to supply conductors 5,6, 7 passing through a glass pinch 8, and are passed to the outsidethrough the glass base 9, to which the glass bulb 10 is sealed. Theenvelope (9, 10) contains N0 (N 0,) vapour at a pressure of about 10-lmm. Hg.

The method according to the invention will now be described more fullywith reference to a few examples.

Example 1 An alloy transistor device comprising a semi-conductive bodyconsisting of p-type silicon provided with a base connection consistingof an alloy of by weight of indium and 10% by weight of copper, andfurther provided with an emitter electrode and a collector electrodeboth consisting of 75% by Weight of gold and 25% by weight of antimonywas etched for about twenty seconds in a bath containing a mixture of a52% aqueous solution of hydrofluoric acid and a 97% aqueous solution ofnitric acid in the volume ratio 1:3 and subsequently washed in streamingdistilled deionised water and dried. Subsequent to the etchingtreatment, the transistor was arranged in a glass envelope containingdry nitrogen dioxide (di-nitrogen-tetroxide). The current amplificationfactor a which amounted to 5 after the etching treatment, rose by thistreatment almost immediately to a value 15. Then water vapour wasintroduced into the envelope to a quantity of less than 1% of the N0content, which increased a further to the value 18. During the pumpingout of this gaseous mixture a increased further to attain a maximumvalue of 22 at a pressure of about 10- mm. Hg, after which the glassenvelope was sealed tight. In order to check the stability of thetransistor, the structure was then heated, so that ar increasedcontinuously until at C. a maximum value of 50 was attained. During thecooling to room temperature the same range of variations was reversed,which confirms the stability of the transistor.

Example 2 An alloy transistor comprising a semi-conductive bodyconsisting of n-type germanium, provided with a base connectionconsisting of an alloy of 97% by weight of tin and 3% by weight ofantimony, and further provided with an emitter electrode and a collectorelectrode both consisting of indium, was etched in a bath composed of 2volume parts 52% aqueous solution of HF, 2 volume parts 97% aqueoussolution of HN and volume parts H 0, and subsequently washed indistilled deionised water and dried. The transistor had a currentamplification factor of 15.2 after this etching operation.The-transistor was subsequently arranged in an envelope containing drynitrogen dioxide (di-nitrogen-tetroxide) at a pressure of about mm. Hg.Owing to this treatment u increased almost immediately to 32. By addingmoist nitrogen dioxide (di-nitrogen-tetroxide) a increased further tothe value 40 at a NO (N O pressure of about 10- mm. Hg and a watervapour pressure of about 10' mm. Hg. After sealing the transistor in aglass envelope the structure was heated to 65 C., at which temperature06 attained the value 41.5; during cooling to room temperature about thesame range of variations was reversed, and at room temperature ea haddecreased to a value of about 40, which confirms the good stability ofthe transistor.

What is claimed is:

l. A method of manufacturing a semi-conductive device comprising asemi-conductive body and plural electrode connections to said body andpossessing a current amplification factor whose value depends on thesurrounding atmosphere, comprising the steps of etching the body, andthereafter introducing the body with its electrode connections into anatmosphere containing a nitrogenoxygen compound.

2. A method of manufacturing a semi-conductive device comprising asemi-conductive body selected from the group consisting of germanium andsilicon and having ohmic and rectifying electrode connections to saidbody, comprising etching the body, and thereafter introducing the bodywith its electrode connections into an atmosphere containing anitrogen-oxygen compound.

3. A method as set forth in claim 2 wherein the atmosphere also containswater vapor.

4. A method as set forth in claim 2 wherein the atmosphere is partlyremoved and then the body with its electrode connections sealed-off in avacuum-tight envelope.

5. A semi-conductive device comprising an etched semi-conductive bodywith plural electrode connections to said body and possessing a currentamplification factor whose value depends on the surrounding atmosphere,a sealed envelope enclosing the body with its connections, and anatmosphere in said envelope comprising a nitrogen-oxygen compound.

6. A semi-conductive device comprising an etched semi-conductive bodyselected from the group consisting of germanium and silicon, ohmic andrectifying electrode connections to said body, a vacuum-tight sealedenvelope enclosing the body with its connections, and an atmosphere insaid envelope comprising a nitrogen-oxygen compound.

7. A device as set forth in claim 6 wherein the nitrogen-oxygen compoundis selected from the group consisting of nitrogen dioxide anddi-nitrogen-tetroxide.

8. A device as set forth in claim 6 wherein the atmosphere includesWater vapor.

9. A device as set forth in claim 8 wherein the pressure of theatmosphere is below 10- mm. of mercury, and the semi-conductive body issilicon.

References Cited in the file of this patent UNITED STATES PATENTS2,812,480 Ellis Nov. 5, 1957

1. A METHOD OF MANUFACTURING A SEMI-CONDUCTIVE DEVICE COMPRISING ASEMI-CONDUCTIVE BODY AND PLURAL ELECTRODE CONNECTIONS TO SAID BODY ANDPOSSESSING A CURRENT AMPLIFICATION FACTOR WHOSE VALUE DEPENDS ON THESURROUNDING ATMOSPHERE, COMPRISING THE STEPS OF ETCHING THE BODY, ANDTHEREAFTER INTRODUCING THE BODY WITH ITS ELECTRODE CONNECTIONS INTO ANATMOSPHERE CONTAINING A NITROGENOXYGEN COMPOUND.